My grandmother's generation (in South Wales) would always make instant coffee using only hot milk. I would ask for it made with water, but she wouldn't dream of doing that for a guest, for fear of appearing mean.

As far as I'm concerned, there are no issues. With a suitable mug, you can heat the milk in situ in the microwave.

I usually just take a bottle (I have an eco-friendly aluminum bottle) and fill it with milk. Then I add some instant coffee, a tiny bit of sugar(helps the grinds dissolve), and some cinnamon or cocoa powder (to flavor). After that I just shake the bottle until it is mixed up very well. The ratio to how much of each ingredient depends on taste. And heating is really optional depending on how well you shake it. During the summer I usually don't heat my coffee because... well it's hot during the summer.

One of my fave summer drinks - dissolve instant coffee in a tablespoon or so of water, add half a glass of cold milk and a squirt of chocolate syrup, stir really well, top up with more cold milk.
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Kate GregoryAug 3 '11 at 12:43

I put milk in a saucepan for 4-5 minutes on medium heat. When I come back, the milk usually has a "skin" on it. Remove that with a spoon, and then pour the milk into the cup. I add a healthy spoonful of instant granules and some sugar, and it's as good as any coffeehouse leche...and way cheaper.

The only thing you might want to consider if you are thinking of adding it to hot milk is a chance of splitting the milk. I would suggest you mix it with a tablespoon of hot water before adding the milk. Less change of splitting.

I add the instant coffee BEFORE heating the milk in the microwave for 2 1/2 minutes. The coffee disolves better in the milk that way. Also, I used rice milk or not regular milk, so it can be compared to skim milk in terms of consistency. For even more added flavor I will add either cocoa powder or chocolate syrup.

I also add the instant coffee before heating the milk. It does make the instant coffee dissolve better. Oddly enough, I also heat the milk for 2:30-2:45 like Melissa. To top it off, I then add a creamer like International Delight into the brew and then mix it all together. It is absolutely divine. I personally don't like the taste of coffee that has been brewed in water. It is too bitter for me. Making it with milk seems to take away the bitterness and only leave the coffee flavor and whatever creamer I have added.

I grew up in Ireland & we drank this as kids. It was made with Sanka. This was easy to make, just pour milk into a sauce pan and then watch it to make sure it did not boil over. Then we would throw instant coffee and sugar into the pot, stir it up, pour it into mugs and drink it. Then we would make another batch 'lol' because even to a child's pallet it's 'friggen' great